Periscope, Telemeter and Perimeter

Periscope
A Periscope is a scientific instrument for observation from a concealed position.

Telemeter
A Telemeter is a scientific instrument for measuring distance from observer.

Perimeter
A perimeter is the length of boundaries or outer lines of an object. For example,

The perimeter of this rectangle is:
Perimeter = 4 + 4 + 2 + 2 = 12 inches

DIFFERENCE BETWEEN
— Microscope and Telescope
— Element and Molecule